Carbon Nanotubes too Weak for Space Elevators

For want of an atom, the space elevator failed

Carbon nanotubes (CNTs) are famed for being a future wonder material that will enable a swathe of super-strong but light applications from racing bikes to computer components.

But now it seems a single out-of-place atom is enough to cut their strength by more than half. That means one of the more outlandish applications for CNT fibres – a sci-fi space elevator – might never happen.

The tubes’ strength is a result of their atomic structure, with walls made from just a single layer of carbon atoms locked in a hexagonal grid. Theoretical studies suggest that a single CNT can have a tensile strength of 100 gigapascals (GPa), making it one of the strongest materials around, but efforts to spin multiple nanotubes into a practical large-scale fibre have only produced ropes with strengths of 1 GPa.

To find out why, Feng Ding of the Hong Kong Polytechnic University and his colleagues simulated CNTs with a single atom is out of place, turning two of the hexagons into a pentagon and heptagon, and creating a kink in the tube. They found this simple change was enough to cut the ideal strength of a CNT to 40 GPa, with the effect being even more severe when they increased the number of misaligned atoms.

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